Golf ball

ABSTRACT

The object of the present invention is to provide a golf ball excellent in resilience, abrasion-resistance and durability by using a novel anion polyurethane ionomer. 
     The golf ball of the present invention is a golf ball having a core and a cover covering the core, comprising a resin component constituting the core or the cover containing a polyurethane ionomer wherein an anionic group is bonded to at least a part of nitrogen atoms constituting a urethane bond or a urea bond in a polyurethane main-chain structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a golf ball, more particularly a golf ball using a novel polyurethane ionomer.

2. Description of the Related Art

As a base resin constituting a cover of a golf ball, ionomer resin, polyurethane and the like are used. The covers containing ionomer resins are widely used because they are excellent in resilience, durability and workability, but problems such as poor shot feeling, insufficient spin performance, and poor controllability due to having high rigidity and hardness are pointed out. On the other hand, polyurethane is used as a base resin constituting a cover since it provides a better shot feeling and spin performance compared to an ionomer resin. For example, U.S. Pat. No. 3,395,109 and U.S. Pat. No. 4,248,432 disclose a use of a thermoplastic polyurethane for a cover. However, a golf ball using the thermoplastic polyurethane for a cover is not yet sufficient in abrasion-resistance, shot feeling, resilience and the like. Therefore, some attempts have been made to covert polyurethane into an ionomer (e.g. U.S. Pat. No. 5,691,066, Japanese Patent Publication No.2002-521157 A, Japanese Patent Publication No. 2003-327652 A).

U.S. Pat. No. 5,691,066 discloses a cationic polyurethane ionomer as a cover material of a golf ball, but because it has poor molding ability, its use is limited. Each of Japanese Patent Publication No. 2002-521157 A and Japanese Patent Publication No. 2003-327652A discloses an anionic polyurethane ionomer, but it tends to be fragile, and some improvement of abrasion-resistance is needed.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above circumstances. The object of the present invention is to provide a golf ball excellent in resilience, abrasion-resistance and durability by using a novel anionic polyurethane ionomer.

A golf ball of the present invention that has solved the above problems is a golf ball having a core and a cover covering the core, wherein a resin component constituting the core or the cover contains a polyurethane ionomer which has an anionic group bonded to at least a part of nitrogen atoms constituting a urethane bond or a urea bond in the main chain structure of the polyurethane. Namely, the present inventors have found that if an anionic group is bonded to a nitrogen atom constituting a urethane bond or a urea bond in the main chain structure of the polyurethane to convert into an ionomer, the polyurethane molecular chains can be bonded to each other through the ionic bond to have even better mechanical property compared with the polyurethane molecular chains hydrogen-bonded to each other by a urethane bond or a urea bond, and accomplished the present invention.

The polyurethane ionomer used in the present invention preferably has the structure shown in Formula (1) and/or Formula (2). In Formula (1):

R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an anionic group; and M is a metal ion of any one of the groups 1 to 17. In Formula (2):

R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an Anionic group; and M is a metal ion of any one of the groups 1 to 17.

The anionic group of the polyurethane ionomer is preferably an anionic group derived from an acid selected from the group consisting of a carboxylic acid, a sulfonic acid, a phosphoric acid, and a sulfuric acid. The polyurethane ionomer can be obtained by, for example, reacting the thermoplastic polyurethane with 1,3-propanesultone.

The present invention provides a golf ball which is excellent in resilience, abrasion-resistance and durability.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a golf ball having a core and a cover covering the core, wherein a resin component constituting the core or the cover contains a polyurethane ionomer which has an anionic group bonded to at least a part of nitrogen atoms constituting a urethane bond or a urea bond in the main chain structure of the polyurethane.

First, the polyurethane ionomer which has an anionic group bonded to at least a part of nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane used in the present invention is explained. The polyurethane ionomer used in the present invention is not particularly limited as long as it has a plurality of polyurethane bonds in a molecule wherein the anionic group is bonded to at least a part of nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane. For example, there is an embodiment wherein the urethane bond is present in the main chain structure of the polyurethane, and the anionic group is bonded to at least a part of nitrogen atoms constituting the urethane bond; and an embodiment wherein the urethane bond and the urea bond are present in the main chain structure of the polyurethane and the anionic group is bonded to at least a part of nitrogen atoms constituting at least one of either the urethane bond or the urea bond.

The anionic group can be bonded directly or indirectly to nitrogen atoms constituting the urethane bond or the urea bond, more preferably indirectly bonded to nitrogen atoms constituting the urethane bond or the urea bond. An embodiment wherein the anionic group is indirectly bonded to the nitrogen atom constituting the urethane bond or the urea bond include, for example, a structure shown by the following Formula (1) and/(2). In Formula (1):

R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an anionic group; and M is a metal ion of any one of the groups 1 to 17.

Formula (1) shows the urethane bond in the main chain structure of the polyurethane, wherein the anionic group Z is indirectly bonded to the nitrogen atom constituting the urethane bond via R. The urethane bond herein is not particularly limited, and it is, for example, a reaction product between a polyisocyanate component and a polyol component constituting the polyurethane.

R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an anionic group; and M is a metal ion of any one of the groups 1 to 17.

Formula (2) shows the urea bond in the main chain structure of the polyurethane, wherein the anionic group is indirectly bonded to the nitrogen atom constituting the urea bond via R. Herein, the urea bond is not particularly limited, and it is, for example, a reaction product of the polyisocyanate component and a polyamine component constituting polyurethane or water (or humid: water in the atmosphere).

In Formulae (1) and (2), as R which is a bivalent hydrocarbon group having 1 to 20 carbon atoms, preferably 2 to 18 carbon atoms, or one in which apart of hydrogen is substituted, any of either an aliphatic hydrocarbon or an aromatic hydrocarbon group is accepted, and a part of hydrogen therein may be substituted. Examples of the bivalent aliphatic hydrocarbon group include a straight-chain aliphatic hydrocarbon group such as a methylene group, an ethylene group, a trimethylene group, a tetramethylene group, a pentamethylene group, a hexamethylene group, a hepta methylene group, and an octamethylene group; a branched aliphatic hydrocarbon group such as a propylene group, an ethyl ethylene group, a dimethyl ethylene group, a methyl trimethylene group, an ethyltrimethylene group, and a dimethyltrimethylene group; and a cyclic aliphatic hydrocarbon group such as a cyclopentylene group and a cyclohexylene group. Examples of the bivalent aromatic hydrocarbon group include an aromatic hydrocarbon group such as an o-phenylene group, an m-phenylene group, a p-phenylene group, a tolylene group, and a xylylene group. A part of hydrogen in the bivalent hydrocarbon group having 1 to 20 carbon atoms maybe substituted with a halogen atom, a nitrile group, and a nitro group.

As the anionic group denoted by Z, preferred is an anionic group derived from an acid selected from the group consisting of the carboxylic acid, the sulfonic acid, a phosphoric acid and a sulfuric acid. More specifically, an anionic group such as COO⁻, SO₃ ⁻, HPO₃ ⁻, and SO₄ ² ⁻ are preferred.

Examples of the metal ion of any one of the groups 1 to 17 denoted by M include Li⁺, Na⁺, K⁺, Mg²⁺, Zn²⁺, Ca²⁺, Mn²⁺, Al³⁺, Ti⁺, Zr⁺, W⁺, and Hf⁺. Among them, Li⁺, Na⁺, K⁺, Mg²⁺ and Zn²⁺ are preferred.

The polyisocyanate component constituting the polyurethane ionomer is not particularly limited as long as it has at least two isocyanate groups, and examples include an aromatic polyisocyanate such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate (TODI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), paraphenylene diisocyanate (PPDI); an alicyclic polyisocyanate or an aliphatic polyisocyanate such as 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI) and norbornene diisocyanate (NBDI). These may be used alone or as a mixture of two or more.

In view of improving abrasion-resistance, as the polyisocyanate component of the polyurethane, it is preferred to use an aromatic polyisocyanate. By using the aromatic polyisocyanate, the mechanical property of the resultant polyurethane is improved, and the cover which is excellent in abrasion-resistance can be obtained. Further, in view of improving the weather resistance, as the polyisocyanate component of the polyurethane, it is preferred to use non-yellowing type polyisocyanate such as TMXDI, XDI, HDI, H₆XDI, IPDI, H₁₂MDI and NBDI, more preferably 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI). It is because 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) has a rigid structure, so that the mechanical property of the resultant polyurethane is improved, and the cover which is excellent in abrasion-resistance can be obtained.

The polyol component constituting the polyurethane ionomer is not particularly limited as long as it has a plurality of hydroxyl group, and such examples include a low-molecular weight polyol and a high-molecular weight polyol. Examples of the low-molecular weight polyol include a diol such as ethylene glycol, diethylene glycol, triethylene glycol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol and 1,6-hexanediol; and a triol such as glycerin, trimethylol propane, and hexanetriol. Examples of the high-molecular weight polyol include a polyether polyol such as polyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), and polyoxytetramethylene glycol; a condensed polyester polyol such as polyethylene adipate (PEA), polybutylene adipate (PBA), and polyhexamethylene adipate (PHMA); a lactone polyester polyol such as poly-ε-caprolactone (PCL); a polycarbonate polyol such as polyhexamethylene carbonate; and an acrylic polyol. The above polyols may be used alone or as a mixture of two or more.

The average molecular weight of the high-molecular weight polyol is not particularly limited, and for example, it is preferably 400 or more, more preferably 1,000 or more. If the average molecular weight of the high-molecular weight polyol is too small, the resultant polyurethane becomes too hard and the shot feeling of the golf ball is lowered. The upper limit of the molecular weight of the high molecular weight polyol is not particularly limited, and it is preferably 10,000, more preferably 8,000.

Additionally, the polyurethane ionomer of the present invention can contain, when necessary, a polyamine as a constitutional component. If the polyamine is used as the constitutional component, the polyamine reacts with the polyisocyanate to generate the urea bond in the main chain structure of the polyurethane. The embodiment wherein the anionic group is bonded to the nitrogen atom constituting the urea bond is also included in the present invention.

The polyamine is not particularly limited as long as it has at least two amino groups, and such examples include an aliphatic polyamine such as ethylenediamine, propylenediamine, butylene diamine and hexamethylenediamine, an alicyclic polyamine such as isophoronediamine and piperazine, and an aromatic polyamine.

The aromatic polyamine is not particularly limited as long as it has at least two amino groups directly or indirectly bonded to an aromatic ring. Herein, “indirectly bonded” means that the amino group is bonded to the aromatic ring via, for example, the lower alkylene group. The aromatic polyamine may be, for example, a monocyclic aromatic polyamine wherein two or more amino groups are bonded to an aromatic ring, or a polycyclic aromatic polyamine containing two or more aminophenyl groups wherein at least an amino group is bonded to the aromatic ring.

Examples of the monocyclic aromatic polyamine are a type such as phenylenediamine, toluenediamine, diethyltoluenediamine, or dimethylthiotoluenediamine where the amino groups are directly bonded to the aromatic ring; and a type such as xylylenediamine where the amino groups are bonded to an aromatic ring through a lower alkylene group. The polycyclic aromatic polyamine may include polyaminobenzene having at least two aminophenyl groups directly bonded to each other or a compound having two aminophenyl groups bonded to each other through a lower alkylene group or an alkylene oxide group. Among them, diaminodiphenylalkane having two aminophenyl groups bonded to each other through a lower alkylene group is preferable. Typically preferred are 4,4′-diaminodiphenylmethane and derivatives thereof.

The synthesis method of the polyurethane ionomer used in the present invention comprises, for example, reacting a thermoplastic polyurethane with 1,3-propanesultone (1,3-propanesultone). Also, in addition to 1,3-propanesultone (1,3-propanesultone), or instead of 1,3-propanesultone (1,3-propanesultone), β-propiolactone may be used. More specifically, the method comprises dissolving a thermoplastic polyurethane into dimethyl acetamide and dispersing NaH and adding 1,3-propanesultone to obtain a polyurethane ionomer which has a sulfonic ion bonded via a trimethylene group to the nitrogen atom constituting the urethane bond or the urea bond as the anionic group Z. The above reaction is not particularly limited, and it is preferably performed at a temperature of −20° C. or more, more preferably −10° C. or more, and preferably at a temperature of 10° C. or less, more preferably 0° C. or less for preferably 0.5 to 4 hours, more preferably 1 to 2 hours. The synthesis method of the polyurethane ionomer used in the present invention is disclosed in detail, for example, in Susan A. Visser and Stuart L. Cooper, “Comparison of the Physical Properties of Carboxylated and Sulfonated Model Polyurethane Ionomers,” Macromolecules 1991,24, 2576-2588.

In the polyurethane ionomer used in the present invention, the ratio of the nitrogen atoms to which the anionic group are bonded to all the nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane can be calculated from the molar quantity of the polyisocyanate component and the molar quantity of 1,3-propanesultone to be used. The ratio of the nitrogen atoms to which the anionic group are bonded to all the nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane is, preferably 0.5 to 50 mol %, more preferably 1 to 25 mol % of all the nitrogen atom constituting the urethane bond or the urea bond (preferably all the nitrogen atom constituting the urethane bond).

The slab hardness of the polyurethane ionomer used in the present invention is preferably 70 or more, more preferably 75 or more, even more preferably 80 or more in Shore A hardness. If it is too soft, the amount of spin becomes so large that the flying distance becomes lowered. Further, the slab hardness is preferably 97 or less, more preferably 95 or less, even more preferably 90 or less in Shore A hardness. If it is too hard, the amount of spin becomes less so that the controllability tends to be lowered. The slab hardness of the polyurethane ionomer can be controlled by suitably selecting the content ratio of the polyisocyanate and the polyol constituting the polyurethane, and the type of the polyol. Herein, the slab hardness of the cover layer means a hardness obtained by measuring the hardness of the polyurethane ionomer molded into the sheet shape. The details of the method to measure the slab hardness is described later.

The golf ball of the present invention is the golf ball having the core and the cover covering the core. It is not particularly limited as long as the resin component constituting the core or the cover contains the above-described polyurethane ionomer. Examples include an embodiment of a two-piece golf ball having a core and a cover covering the core wherein the resin component constituting the cover contains the polyurethane ionomer; an embodiment of a three-piece golf ball having a core, an intermediate layer covering the core and a cover covering the intermediate layer wherein the resin component constituting the cover or the intermediate layer contains the polyurethane ionomer; an embodiment of a multi-piece golf ball having a core and a cover and at least two intermediate layer between the core and the cover wherein the resin component constituting the cover or at least one layer of the intermediate layer contains the polyurethane ionomer; or an embodiment of a wound-core golf ball having a wound core and a cover wherein the resin component constituting the cover contains the polyurethane ionomer. The present invention can be applied to all types of the golf ball. Herein, in a structure of a golf ball, a combination of a core and an intermediate layer may sometimes be referred to as multi layer core, and a combination of a cover and an intermediate layer may sometimes be referred to as multi layer cover. Among them, the two-piece golf ball, the three-piece golf ball and the multi-piece golf ball are the preferred embodiments of the present invention.

The golf ball of the present invention preferably comprises a cover containing the polyurethane ionomer as the resin component, and the content of the polyurethane ionomer in the resin component constituting the cover is preferably 50 mass % or more, more preferably 70 mass % or more, even more preferably 90 mass % or more. Further, according to the preferred embodiment, the resin component constituting the cover essentially consists of the polyurethane ionomer.

The embodiment of the polyurethane ionomer may be any of either so-called thermoplastic polyurethane or thermosetting polyurethane. The golf ball excellent in abrasion-resistance, durability and resilience can be obtained in any of the embodiments. Herein, the thermoplastic polyurethane means a polyurethane which shows plasticity by the application of heat, generally having a straight-chain structure polymerized to a certain degree of higher molecular weight. On the other hand, the thermosetting polyurethane (two-component curing type polyurethane) is a polyurethane obtained by putting a low-molecular weight urethane prepolymer aside once, and reacting the prepolymer with a chain extender (curing agent) for polymerization to higher molecular, just before molding the cover. By controlling the number of functional groups in the prepolymer and the chain extender (curing agent) used in the thermosetting polyurethane, a polyurethane having a straight-chain structure or a polyurethane having a three-dimensional cross-linked structure can be contained. In the present invention, a thermoplastic polyurethane ionomer is preferably used because the molding of the cover becomes easy therewith.

In the present invention, other than the polyurethane ionomer, the resin component that can be used as the cover composition include a thermoplastic resin, a thermoplastic elastomer, a diene type block copolymer and the like. The thermoplastic resin includes an ionomer resin, and examples of the ionomer resin include one prepared by neutralizing at least a part of carboxyl groups in a copolymer composed of ethylene and α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms with a metal ion, one prepared by neutralizing at least a part of carboxyl groups in a ternary copolymer composed of ethylene, α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and α,β-unsaturated carboxylic acid ester with a metal ion, or a mixture thereof. The specific examples of the ionomer resin include Himilan available from MITSUI-DUPONT POLYCHEMICAL, Surlyn available from DUPONT CO., and Iotek available from ExxonMobil Corp.

The specific examples of the thermoplastic elastomer include a thermoplastic polyamide elastomer having a commercial name of “PEBAX”, for example, “PEBAX 2533” available from ARKEMA Inc, a thermoplastic polyester elastomer having a commercial name of “HYTREL”, for example, “HYTREL 3548”, and “HYTREL 4047” available from DU PONT-TORAY Co., and a thermoplastic polystyrene elastomer having a commercial name of “Rabalon” available from Mitsubishi Chemical Co. Among them, a thermoplastic polystyrene elastomer is preferred. Examples of the thermoplastic polystyrene elastomer include a polystyrene block component as a hard segment, and as a soft segment, a polystyrene-diene type block copolymer having a diene block component such as polybutadiene, isoprene, hydrogenated polybutadiene, and hydrogenerated polyisoprene. The polystyrene-diene type block copolymer preferably has a double bond derived from a conjugated diene compound of a block copolymer or a partially hydrogenated block copolymer. Examples of the polystyrene-diene type block copolymer include a block copolymer of the SBS (styrene-butadiene-styrene) structure having a polybutadiene block, or a block copolymer of the SIS (styrene-isoprene-styrene) structure.

The cover for a golf ball of the present invention may contain, other than the above-mentioned resin component, pigment component such as a white pigment (titanium oxide) and a blue pigment, a gravity adjusting agent such as calcium carbonate and barium sulfate, a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent material or a fluorescent brightener to the extent that the cover performance is not damaged.

The amount of the white pigment (titanium oxide) to be blended is preferably 0.5 part by mass or more, more preferably 1 part by mass or more and preferably 10 parts by mass or less, more preferably 8 parts by mass or less based on 100 parts by mass of the resin component constituting the cover. The white pigment in an amount of 0.5 part by mass or more provides opacity to the cover, while the white pigment in an amount of more than 10 parts by mass may lower the durability of the resultant cover.

The cover for a golf ball of the present invention can be prepared by molding the cover composition containing the above-mentioned cover materials. Examples of a method for molding a cover include a method wherein the cover composition is subjected to compression molding into hollow-shell shape, and the core is covered with a plurality of shells (preferably a method wherein a cover composition is compression-molded into hollow-half shell shape and the core is covered with two half shells), and a method wherein the cover composition is subjected to direct injection molding onto the core.

Molding of the half shell can be performed by either compression molding method or injection molding method, and the compression molding method is preferred. The compression-molding of the cover composition into half shell can be carried out, for example, under a pressure of 1 MPa or more and 20 MPa or less at a temperature of −20° C. or more and 70° C. or less relative to the melt flow temperature of the cover composition. By performing the molding under the above conditions, a half shell having a uniform thickness can be formed. Examples of a method for molding the cover using half shells include compression molding by covering the core with two half shells. The compression molding of half shells into the cover can be carried out, for example, under a pressure of 0.5 MPa or more and 25 MPa or less at a temperature of −20° C. or more and 70° C. or less relative to the melt flow temperature of the cover composition. By performing the molding under the above conditions, a cover for a golf ball having a uniform thickness can be formed.

According to the present invention, the cover composition can be subjected to injection molding directly onto the core. In such a case, it is preferred to use upper and lower molds for forming a cover having a spherical cavity and pimples, wherein a part of the pimple also serves as a retractable hold pin. When forming the cover by injection molding, the hold pin is protruded to hold the core, and the cover composition is fed to cool to obtain a cover. For example, the cover composition heated to 200° C. to 250° C. is charged into a mold held under the pressure of 9 MPa to 15 MPa in 0.5 to 5 seconds. After cooling for 10 to 60 seconds, the mold is opened and the golf ball with the cover molded is taken out from the mold, and as necessary, is preferably subjected to surface treatment such as deburring, cleaning, and sandblast. If desired, a paint film or a mark may be formed.

The thickness of the cover of the golf ball of the present invention is not particularly limited, and it is preferably 0.3 mm or more, more preferably 0.4 mm or more, even more preferably 0.5 mm or more. If the thickness of the cover is too thin, the abrasion-resistance tends to be lowered. Further, the thickness of the cover is preferably 2.3 mm or less, more preferably 2.1 mm or less, even more preferably 1.9 mm or less. If the thickness of the cover is too large, the resilience tends to be lowered.

The slab hardness of the cover for a golf ball of the present invention is preferably 25 or more, more preferably 30 or more, even more preferably 35 or more, and preferably 70 or less, more preferably 65 or less, even more preferably 60 or less in shore D hardness. If the slab hardness of the cover is 25 or more, the rigidity of the resultant cover can be enhanced, and the golf ball excellent in resilience (flying distance) can be obtained. On the other hand, if the slab hardness is 70 or less, the shot feeling of the golf ball when hitting the ball can be enhanced. Herein, the slab hardness of the cover means a hardness obtained by measuring the hardness of the cover composition molded into the sheet shape. The details of the method to measure the slab hardness is described later.

Next, preferred embodiments of the golf ball core (including multi layer core) of the present invention are explained. The diameter of the core of a golf ball of the present invention is preferably 39.0 mm or more, more preferably 39.5 mm or more, even more preferably 40.8 mm or more. If the diameter of the core is less than 39.0 mm, the thickness of the cover becomes too thick, so that the resilience is lowered. The upper limit of the diameter of the core is not particularly limited, but it is preferably 42.2 mm, more preferably 42.0 mm, even more preferably 41.8 mm. If the diameter of the core is more than 42.2 mm, the cover becomes relatively too thin, so that the protection effects of the cover cannot be sufficiently obtained.

Further, a compression deformation amount of the core when applying a load from 98 N as an initial load to 1275 N as a final load is preferably 2.50 mm or more, more preferably 2.60 mm or more, even more preferably 2.70 mm or more. If the above deformation amount is too small, the core becomes too hard, so that the shot feeling tends to be lowered. On the other hand, the upper limit of the compression deformation amount when applying a load from the initial load of 98 N to the final load of 1275 N is not particularly limited, but is preferably 3.20 mm, more preferably 3.10 mm, even more preferably 3.00 mm. If the above deformation amount is too large, the core becomes too soft, so that the shot feeling may feel too heavy.

It is also a preferred embodiment of the present invention to use, as the core of the golf ball, a core having the surface hardness larger than the center hardness. For example, by employing a multi layer core structure, the surface hardness of the core larger than the center hardness thereof can be readily obtained. The difference of the hardness between the surface hardness and the center hardness of the core is preferably 20 or more, more preferably 25 or more in shore D hardness. If the surface hardness of the core is larger than the center hardness thereof, the launch angle becomes higher and the amount of spin becomes lowered, so that the flying distance is improved. The upper limit of the difference in shore D hardness between the surface hardness and the center hardness is not particularly limited, and is preferably 40, more preferably 35. If the hardness becomes too large, the durability tends to be lowered.

The center hardness of the core is preferably 30 or more, more preferably 32 or more, even more preferably 35 or more in shore D hardness. If the center hardness of the core is less than 30 in shore D hardness, the core becomes too soft, so that the resilience may become lowered. Additionally, the center hardness of the core is preferably 50 or less, more preferably 48 or less, even more preferably 45 or less in shore D hardness. If the center hardness is more than 50 in shore D hardness, the core becomes too hard, so that the shot feeling tends to be lowered. In the present invention, the center hardness of the core means the hardness obtained by measuring the central point of the cut surface of the core cut into halves with the Shore D type spring hardness tester.

The surface hardness of the core of the golf ball of the present invention is preferably 45 or more, more preferably 50 or more, even more preferably 55 or more in shore D hardness. If the above hardness is less than 45, the core becomes so soft that the resilience may become lowered. Further, the surface hardness of the core is preferably 65 or less, more preferably 62 or less, even more preferably 60 or less in shore D hardness. If the surface hardness is more than 65 in shore D hardness, the core becomes so hard that the shot feeling may become lowered.

As the core for the two-piece golf ball, any core which is well-known can be employed. The core of the two-piece golf ball, for example, without limitation, is preferably a molded body which is formed by heat-pressing a rubber composition for the core. The rubber composition for the core comprises, for example, a base rubber, a crosslinking initiator, a co-crosslinking agent and a filler.

The base rubber preferably includes a natural rubber and/or a synthetic rubber. Examples of the base rubber are butadiene rubber (BR), ethylene-propylene-diene terpolymer (EPDM), isoprene rubber (IR), styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR). Among them, butadiene rubber, particularly cis-1,4-polybutadiene, is preferable in view of its superior repulsion property. Typically preferred is the high cis-polybutadiene rubber having cis-1,4 bond in a proportion of not less than 40%, more preferably not less than 70%, even more preferably not less than 90%.

The crosslinking initiator is blended to crosslink the base rubber component. As the crosslinking initiator, an organic peroxide is preferably used. Examples of the organic peroxide for use in the present invention are dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Among them, dicumyl peroxide is preferable. The amount of the organic peroxide to be blended in the rubber composition is preferably 0.2 part by mass or more, more preferably 0.3 part by mass or more, and preferably 3 parts by mass or less, more preferably 2 parts by mass or less based on 100 parts by mass of the base rubber. If the content is less than 0.2 part by mass, the core becomes too soft, and the resilience tends to be lowered, and if the content is more than 3 parts by mass, the amount of co-crosslinking agent needs to be increased in order to obtain an appropriate hardness, so that the resilience tends to be insufficient.

The co-crosslinking agent is not particularly limited as long as it has the effect of crosslinking a rubber molecule with a base rubber molecular chain by graft polymerization; for example, α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms or a metal salt thereof, more preferably, acrylic acid, methacrylic acid or a metal salt thereof may be used. As the metal constituting the metal salt, for example, zinc, magnesium, calcium, aluminum and sodium may be used, and among them, zinc is preferred because it provides high resilience. The amount of the co-crosslinking agent to be used is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less relative to 100 parts by mass of the base rubber. If the amount of the co-crosslinking agent to be used is less than 10 parts by mass, the amount of the organic peroxide must be increased to obtain an appropriate hardness which tends to lower the resilience. On the other hand, if the amount of the co-crosslinking agent to be used is more than 50 parts by mass, the core becomes too hard, so that the shot feeling may be lowered.

The filler contained in the rubber composition for the core is mainly one blended as a gravity adjusting agent in order to adjust the specific gravity of the golf ball obtained as the final product in the range of 1.0 to 1.5, and may be blended as required. Examples of the filler include an inorganic filler such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten powder, and molybdenum powder. The amount of the filler to be blended in the rubber composition is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and preferably 50 parts by mass or less, more preferably 35 parts by mass or less based on 100 parts by mass of the base rubber. If the amount of filler to be blended is less than 2 parts by mass, it becomes difficult to adjust the weight, while if it is more than 50 parts by mass, the weight ratio of the rubber component becomes small and the resilience tends to be lowered.

As the rubber composition for the core, in addition to a base rubber, a crosslinking initiator, a co-crosslinking agent and a filler, an organic sulfur compound, an antioxidant or a peptizing agent may be blended as appropriate.

As the organic sulfur compound, a diphenyl disulfide may be preferably used. The amount of the diphenyl disulfide to be blended is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less relative to 100 parts by mass of the base rubber. Examples of the diphenyl disulfide include diphenyl disulfide, a monosubstitution such as bis(4-chlorophenyl)disulfide, bis (3-chlorophenyl)disulfide, bis(4-bromophenyl)disulfide, bis(3-bromophenyl)disulfide, bis(4-fluorophenyl)disulfide, bis(4-iodophenyl)disulfide and bis(4-cyanophenyl)disulfide; a disubstitution such as bis(2,5-dichlorophenyl)disulfide, bis(3,5-dichlorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide, bis(2,5-dibromophenyl)disulfide, bis(3,5-dibromophenyl)disulfide, bis(2-chloro-5-bromophenyl)disulfide, and bis(2-cyano-5-bromophenyl)disulfide; trisubstitution such as bis(2,4,6-trichlorophenyl)disulfide, and bis(2-cyano-4-chloro-6-bromophenyl)disulfide; tetra substitution such as bis(2,3,5,6-tetra chlorophenyl)disulfide; penta substitution such as bis(2,3,4,5,6-pentachlorophenyl)disulfide and bis(2,3,4,5,6-penta bromophenyl)disulfide. These diphenyl disulfides can enhance resilience by having some influence on the state of vulcanization of vulcanized rubber. Among them, diphenyl disulfide and bis(penta bromophenyl)disulfide are preferably used since a golf ball having particularly high resilience can be obtained.

The amount of the antioxidant to be blended is preferably 0.1 part by mass or more and 1 part by mass or less based on 100 parts by mass of the base rubber. Further, the peptizing agent is preferably 0.1 part by mass or more and 5 parts by mass or less based on 100 parts by mass of the base rubber.

The conditions for press-molding the rubber composition should be determined depending on the rubber composition. The press-molding is preferably carried out for 10 to 60 minutes at the temperature of 130 to 200° C. Alternatively, the press-molding is preferably carried out in a two-step heating, for example, for 20 to 40 minutes at the temperature of 130 to 150° C., and continuously for 5 to 15 minutes at the temperature of 160 to 180° C.

In the present invention, the core which has been formed as described above is covered with the cover composition containing the resin component, an additive and the like to form a golf ball body. When a thermosetting polyurethane is used as the resin component constituting the cover, the cover may be formed by, for example, charging the cover composition into the mold having the spherical shape with the resultant core retained in the mold, and then inverting the mold to carry out curing reaction together with another mold having the spherical shape charged with the cover composition. The curing reaction of the cover composition containing thermosetting polyurethane is preferably carried out at a temperature of 30° C. to 120° C., more preferably 50° C. to 80° C. preferably for 2 to 60 minutes, more preferably 5 to 30 minutes.

When a thermoplastic polyurethane which has already been polymerized to higher molecular weight (for example, in the form of pellet) is used as the resin component constituting the cover, for example, a method including previously molding the cover composition into two hemispherical half shells, covering the core together with the two half shells, and subjecting the core with two half shells to the pressure molding at a temperature of 130 to 170° C. for 1 to 5 minutes; and a method including injection-molding the cover composition directly onto the core to form a cover may be employed.

Further, when forming the cover, the cover can be formed with a plurality of concavities, which is so called “dimple”, at the surface thereof. As required, the surface of the golf ball can be subjected to grinding treatment such as sandblast. The golf ball of the present invention is preferably subjected to paint finish, marking with a stamp and the like in order to improve the appearance and the commercial value thereof.

The above method is explained based on an embodiment of a two-piece golf ball. When preparing a wound-core golf ball, wound core may be used, and preparing a multi-piece golf ball comprising at least three layers, an intermediate layer can be formed between the core and the cover.

For preparing a wound golf ball, a conventional wound core can be used in the present invention. The wound core comprises a center and a rubber thread layer which is formed by winding a rubber thread around the center in an elongated state. Examples of the center are a liquid center and a solid center formed of rubber. Examples of the center are a liquid center and a solid center formed of rubber. In the present invention, the rubber thread, which is conventionally used for winding around the center, can be adopted for winding around the center. The rubber thread, for example, is obtained by vulcanizing a rubber composition including a natural rubber, or a mixture of natural rubber and a synthetic polyisoprene, a sulfur, a vulcanization auxiliary agent, a vulcanization accelerator, and an antioxidant. The rubber thread is wound around the center in elongation of about 10 times length to form the wound core.

When preparing a multi-piece golf ball comprising at least three layers, as the intermediate layer, the layer used for the resin component constituting the cover may be used, including, for example, a thermoplastic elastomer such as the thermoplastic ionomer resin, thermoplastic polyamide elastomer, thermoplastic polyester elastomer, thermoplastic polyurethane elastomer; a diene type block copolymer and a rubber composition. The intermediate layer may further include a gravity adjusting agent such as barium sulfate and tungsten, an antioxidant and a colorant.

As a method of forming the intermediate layer, typically employed is a method including previously molding the intermediate layer composition into two hemispherical half shells, covering the solid core together with the two half shells, and subjecting the core with two half shells to the pressure molding, or a method including injection-molding the cover composition directly onto the solid center to form a cover.

The compression deformation amount of the golf ball of the present invention when applying a load from 98 N as a initial load to 1275N as a final load is preferably 2.1 mm or more, more preferably 2.3 mm or more, even more preferably 2.5 mm or more. If the deformation amount is too small, the shot feeling becomes hard and lowered. The upper limit of the compression deformation amount when applying a load from 98N as a initial load to 1275N as a final load is not particularly limited, and is preferably 4.0 mm, more preferably 3.8 mm, even more preferably 3.5 mm. If the deformation amount becomes too large, the golf ball becomes too soft and the shot feeling may become heavy.

The golf ball of the present invention preferably has a PGA compression of 65 or more, more preferably 70 or more. If the PGA compression is less than 65, the resilience tends to be lowered, and the golf ball becomes too soft so that the shot feeling becomes heavy. The upper limit of the PGA compression is not particularly limited, and is preferably 115, more preferably 110. If the PGA compression is more than 115, the golf ball becomes too hard so that the shot feeling is lowered.

EXAMPLES

The following examples illustrate the present invention, however these examples are intended to illustrate the invention and are not to be construed to limit the scope of the present invention. Many variations and modifications of such examples will exist without departing from the scope of the inventions. Such variations and modifications are intended to be within the scope of the invention.

[Evaluation Method] (1) Abrasion-Resistance

A commercially available pitching wedge was installed on a swing robot available from TRUETEMPER CO., and two points of a ball respectively were hit once at the head speed of 36 m/sec. to observe the areas which were hit. Abrasion-resistance was evaluated and ranked into four levels based on following criteria.

-   E(Excellent): Almost no scratch was present on the surface of the     golf ball. -   G(Good): Slight scratches were present on the surface of the golf     ball. -   F(Fair): The surface of the golf ball was abraded a little, and     scuffing could be observed. -   P(Poor): The surface of the golf ball was abraded considerably, and     scuffing was conspicuous.

(2) Durability

Each golf ball was repeatedly hit with a metal head driver (W#1) attached to a swing robot manufactured by TRUETEMPER CO, at the head speed of 45 m/sec. to make the golf ball collide with a collision board. Times up to which the golf balls are cracked were measured. In addition, each value obtained was reduced to an index number relative to the measured value obtained in Golf ball No. 11 being assumed 100. The larger number indicates better durability.

(3) Slab Hardness of the Cover (Shore A Hardness or Shore D Hardness)

Using the cover composition or polyurethane, a sheet having a thickness of about 2 mm were prepared by hot press molding and preserved at the temperature of 23° C. for two weeks. Three or more of the sheets were stacked on one another to avoid being affected by the measuring substrate on which the sheets were placed, and the stack was subjected to the measurement using P1 type auto hardness tester provided with the Shore A or Shore D type spring hardness tester prescribed by ASTM-D2240, available from KOUBUNSHI KEIKI CO., LTD.

(4) Repulsion Coefficient of Golf Ball

An aluminum cylinder having a weight of 200 g was collided with each golf ball at the speed of 45 m/sec to measure the speed of the cylinder and each of the golf balls before and after the collision to calculate the repulsion coefficient of each golf ball from the speed and the weight thereof. The measurement was carried out five times for each golf ball, and the average was taken as the repulsion coefficient of the golf ball. Each value of the repulsion coefficient was reduced to an index number relative to the value of golf ball No.11 being assumed 100. The larger index number indicates better resilience.

(5) Compression Deformation Amount (mm)

The compression deformation amount (amount shrinks along the compression direction: mm) of the golf balls or the cores was measured when applying a load from 98N (10 kgf) as an initial load to 1275 N (130 kgf) as a final load to the golf balls or the cores.

[Synthesis of Polyurethane Ionomers A to I]

As shown in Table 1, a solution comprising 100 parts by mass of the thermoplastic polyurethane dissolved in 1000 parts by mass of dimethyl acetamide (DMA) was prepared, and 3 parts by mass of NaH was dispersed in the solution. The dispersion liquid was cooled to a temperature of −5° C. to 0° C. while being mixed for 45 minutes. After a predetermined amount of 1,3-propanesultone (1,3-propanesultone) was added, the mixture was gradually heated to a room temperature and was reacted for 2 hours. Then the deposited materials were collected and dried to obtain the polyurethane ionomer wherein the anionic group is bonded to nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane.

TABLE 1 Polyurethane ionomer A B C D E F G H I XNY90A 100  100  100  — — — — — — ET890 — — — 100  100  100  — — — ET690 — — — — — — 100  100  100  1,3-propanesultone  3  6  9  3  6  9  3  6  9 Shore A hardness 92 94 96 93 95 97 91 93 95 Shore D hardness 42 44 47 43 45 48 41 43 46 Formulation: parts by mass Notes on Table 1: ET890: a MDI-PTMG type thermoplastic polyurethane available from BASF Japan ET690: a MDI-adipate type polyester thermoplastic polyurethane available from BASF Japan XNY90A: a H₁₂MDI-PTMG type thermoplastic polyurethane available from BASF Japan

[Synthesis of Polyurethane Ionomers J and K] Polyurethane Ionomer J

324 parts by mass of an polytetramethylene glycol (available from BASF) having a number average molecular weight of 1,000 obtained by ring-opening polymerization of tetrahydrofuran, 78.5 parts by mass of 4,4′-diphenylmethane diisocyanate (4,4′-MDI available from NIPPON POLYURETHANE INDUSTRY,) and 13.1 parts by mass of ethylene glycol solution containing 20% 5-sodium sulfoisophthalate hydroxyl ethyl ester (available from TAKEMOTO OIL & FAT Co., Ltd) were blended to react at the temperature of 70° C. for 30 minutes. Into the resultant urethane prepolymer, 19.5 parts by mass of butanediol (available from KANTO KAGAKU.) and 78.5 parts by mass of methane diisocyanate were added and the mixture was stirred at a high speed; having been mixed sufficiently, the mixture was cast into a tray to react at the temperature of 130° C. for 10 hours to obtain polyurethane ionomer J.

Polyurethane Ionomer K

310 parts by mass of an adipate polyol having a number average molecular weight of 1,000 (produced by KURARAY CO., LTD.), 75 parts by mass of 4,4′-MDI and 12 parts by mass of a ethylene glycol solution containing 20% 5-sodium sulfoisophthalate hydroxylethyl ester (produced by TAKEMOTO OIL & FAT Co., Ltd) were blended to react at the temperature of 70° C. for 30 minutes. Into the resultant urethane prepolymer, 17.8 parts by mass of butanediol (produced by KANTO KAGAKU.) and 75 parts by mass of 4,4′-MDI were added the mixture was stirred at a high speed; having been mixed sufficiently, the mixture was cast into a tray to react at the temperature of 130° C. for 10 hours to obtain polyurethane ionomer K.

[Preparation of Golf Ball] (1) Preparation of Core Core No.1

The rubber composition shown in Table 2 was kneaded and pressed with upper and lower molds each having a spherical cavity at the heating condition of 170° C. for 15 minutes to obtain the core in a spherical shape having a diameter of 40 mm and a weight of 36.7 g.

Core No.2

The rubber composition for the inner layer core shown in Table 2 was kneaded and pressed with upper and lower molds each having a spherical cavity at the heating condition of 170° C. for 15 minutes to obtain the inner layer core in a spherical shape having a diameter of 38.5 mm and a weight of 34.5g. Next, materials for outer layer core shown in Table 2 were mixed using twin-screw kneading extruder to prepare the composition for outer layer core in the form of pellet. Extrusion was conducted in the following conditions: screw diameter=45mm, screw revolutions=200 rpm, screw L/D=35 and the core composition was heated to from 150 to 230° C. at the die position of the extruder.

The composition for the outer layer thus prepared was injection-molded onto the obtained inner core in a spherical shape, thereby obtaining the multi layer core having a diameter of 41.8 mm and a weight of 42.2 g.

TABLE 2 Core composition Core No. 1 Core No. 2 Inner layer Polybutadiene rubber 100 100 Zinc acrylate 33 35 Zinc oxide Appropriate Appropriate amount amount Diphenyl disulfide 0.5 0.5 Dicumyl peroxide 1.0 0.8 Outer layer Himilan 1605 — 50 Himilan 1706 — 50 Property Diameter of core(mm) 40 41.8 Center hardness of core (Shore D) 32 41 Surface hardness of 57 68 core (Shore D) Difference of Core 25 27 hardness (Shore D) Compression 3.1 2.6 deformation amount of core (mm) Formulation: parts by mass The amount of zinc oxide to be blended was suitably adjusted so that the weight of the ball became 45.4 g. Notes on Table 2: Polybutadiene rubber: BR18(containing 96% or more of cis) produced by JSR Zinc acrylate: ZNDA-90S produced by NIHON JYORYU KOGYO Co,. LTD. Zinc oxide: “Ginrei R” produced by Toho-Zinc Co. Dicumyl peroxide: Percumyl produced by NOF Corporation Diphenyl disulfide: produced by Sumitomo Seika Chemicals Company Limited Himilan 1605: a sodium ion-neutralized ethylene-methacrylic acid copolymer ionomer resin available from MITSUI-DUPONT POLYCHEMICAL. Himilan 1706: a zinc ion-neutralized ethylene-methacrylic acid copolymer ionomer resin available from MITSUI-DUPONT POLYCHEMICAL

(3) Preparation of Cover Composition

The cover materials shown in Table 3 were mixed using a twin-screw kneading extruder to obtain the cover composition in the form of pellet. The extrusion was conducted in the following conditions: screw diameter=45 mm, screw revolutions=200 rpm, screw L/D=35, and the cover composition was heated to from 200° C. to 260° C. at the die position of the extruder.

TABLE 3 Golf ball No. 1 2 3 4 5 6 7 8 9 10 11 12 13 Core structure No. 1 No. 1 No. 2 No. 1 No. 1 No. 1 No. 1 No. 1 No. 1 No. 1 No. 1 No. 1 No. 1 Cover composition Polyurethane ionomer A 100 — — — — — — — — — — — — Polyurethane ionomer B — 100 100 — — — — — — — — — — Polyurethane ionomer C — — — 100 — — — — — — — — — Polyurethane ionomer D — — — — 100 — — — — — — — — Polyurethane ionomer E — — — — — 100 — — — — — — — Polyurethane ionomer F — — — — — — 100 — — — — — — Polyurethane ionomer G — — — — — — — 100 — — — — — Polyurethane ionomer H — — — — — — — — 100 — — — — Polyurethane ionomer I — — — — — — — — — 100 — — — Polyurethane ionomer J — — — — — — — — — — 100 — — Polyurethane ionomer K — — — — — — — — — — — 100 — Thermoplastic polyurethane — — — — — — — — — — — — 100 ET690 Titanium oxide 4 4 4 4 4 4 4 4 4 4 4 4 4 Cover hardness 42 44 44 47 43 45 48 41 43 46 42 42 41 (shore D hardness) Golf ball compression 2.90 2.80 2.30 2.70 2.88 2.77 2.65 2.93 2.81 2.72 2.89 2.91 2.92 deformation amount (mm) Evaluation Abration-resistance G E E G G E G G E G F P F Resilience 101 104 107 105 101 103 106 101 103 105 100 98 96 Durability 127 119 125 105 118 114 101 119 113 100 100 95 98 Formulation: parts by mass Notes on Table 3: Thermoplastic polyurethane ET690: MDI-adipate type polyester thermoplastic polyurethane available from BASF Japan (4)Molding of cover Golf balls Nos. 1 and 2 and Nos. 4 to 13

As shown in Table 3, the resultant cover composition was injection-molded onto the core No.1 thus obtained to form the cover covering the core having a thickness of 1.4 mm. The upper and lower molds for forming the cover have a spherical cavity with dimples. The part of the dimples can serve as a hold pin which is retractable. When forming the golf ball body, the hold pins were protruded to hold the core, and the resin heated at 210° C. was charged into the mold held under the pressure of 80 tons for 0.3 seconds. After the cooling for 30 seconds, the molds were opened and then the golf ball body was discharged. Golf ball No.3

As shown in Table 3, molding of half shells were performed by charging the pellet-form cover composition obtained into each of the depressed part of the lower mold for molding half shells, and applying pressure to mold half shells. Compression molding was conducted at the temperature of 170° C. for 5 minutes under the molding pressure of 2.94 MPa. The core No.2 was covered with two half shells thus obtained in a concentric manner and the cover (thickness of 0.5 mm) was molded by compression molding. Compression molding was performed at the temperature of 150° C. for 2 minutes under the molding pressure of 9.8 MPa.

The surface of the obtained golf ball was subjected to the sand-blast treatment, and then the mark was printed and the clear paint was coated on the surface of the golf ball respectively. The paint was dried in an oven kept at 40° C. to obtain the golf ball having a diameter of 42.8 mm and a mass of 45.4 g. The evaluation results of the resultant golf balls with regard to repulsion coefficient, abrasion-resistance and durability are shown in Table 3, too.

Golf balls Nos.1 to 10 are the golf balls having a core and a cover covering the core, wherein the resin component constituting the core or the cover contains the polyurethane ionomer which has the anionic group bonded to at least a part of nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane. All of the golf balls according to the present invention are excellent in abrasion-resistance, resilience and durability. The golf ball Nos.11 and 12 are the golf balls using a conventional polyurethane ionomer, and are inferior to the golf ball of the present invention in abrasion-resistance, resilience and durability. Golf ball No.13 is a golf ball using a conventional thermoplastic polyurethane (not an ionomer). It was inferior to a golf ball of the present invention in abrasion-resistance, resilience and durability.

The present invention provides a golf ball which is excellent in abrasion-resistance, resilience and durability.

This application is based on Japanese Patent application No. 2,006-095,713 filed on Mar. 30, 2006, the contents of which are hereby incorporated by reference. 

1. A golf ball having a core and a cover covering the core, wherein a resin component constituting the core or the cover contains a polyurethane ionomer which has an anionic group bonded to at least a part of nitrogen atoms constituting a urethane bond or a urea bond in the main chain structure of the polyurethane.
 2. The golf ball according to claim 1, wherein the polyurethane ionomer has a structure shown in Formula (1):

wherein R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an anionic group; and M is a metal ion of any one of the groups 1 to
 17. 3. The golf ball according to claim 1, wherein the polyurethane ionomer has a structure shown in Formula (2):

wherein R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an anionic group; and M is a metal ion of any one of the groups 1 to
 17. 4. The golf ball according to claim 1, wherein the anionic group in the polyurethane ionomer is an anionic group derived from an acid selected from the group consisting of a carboxylic acid, a sulfonic acid, a phosphoric acid and a sulfuric acid.
 5. The golf ball according to claim 1, wherein the polyurethane ionomer is a polyurethane ionomer obtained by reacting a thermoplastic polyurethane with 1,3-propanesultone.
 6. The golf ball according to claim 1, wherein a ratio of the nitrogen atoms to which the anionic group are bonded to all the nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane is from 0.5 to 50 mol %
 7. The golf ball according to claim 1, wherein the polyurethane ionomer has a slab hardness of 70 or more in shore A hardness.
 8. The golf ball according to claim 1, wherein the golf ball is a two-piece golf ball having a core and a cover covering the core wherein the resin component constituting the cover contains the polyurethane ionomer.
 9. The golf ball according to claim 1, wherein the golf ball is a three-piece golf ball having a core, an intermediate layer covering the core and a cover covering the intermediate layer wherein the resin component constituting the cover or the intermediate layer contains the polyurethane ionomer
 10. A golf ball having a core and a cover covering the core, wherein a resin component constituting the core or the cover contains a polyurethane ionomer which has an anionic group bonded to at least a part of nitrogen atoms constituting a urethane bond or a urea bond in the main chain structure of the polyurethane, the polyurethane ionomer has structures shown in Formulae (1) and (2):

wherein R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an Anionic group; and M is a metal ion of any one of the groups 1 to 17, and

wherein R is a bivalent hydrocarbon group having 1 to 20 carbon atoms or one in which a part of hydrogen is substituted; Z is an anionic group; and M is a metal ion of any one of the groups 1 to
 17. 11. The golf ball according to claim 10, wherein the anionic group in the polyurethane ionomer is an anionic group derived from an acid selected from the group consisting of a carboxylic acid, a sulfonic acid, a phosphoric acid and a sulfuric acid.
 12. The golf ball according to claim 11, wherein the polyurethane ionomer is a polyurethane ionomer obtained by reacting a thermoplastic polyurethane with 1,3-propanesultone.
 13. The golf ball according to claim 12, wherein a ratio of the nitrogen atoms to which the anionic group are bonded to all the nitrogen atoms constituting the urethane bond or the urea bond in the main chain structure of the polyurethane is from 0.5 to 50 mol %.
 14. The golf ball according to claim 13, wherein the polyurethane ionomer has a slab hardness of 70 or more in shore A hardness.
 15. The golf ball according to claim 14, wherein the golf ball is a two-piece golf ball having a core and a cover covering the core wherein the resin component constituting the cover contains the polyurethane ionomer.
 16. The golf ball according to claim 14, wherein the golf ball is a three-piece golf ball having a core, an intermediate layer covering the core and a cover covering the intermediate layer wherein the resin component constituting the cover or the intermediate layer contains the polyurethane ionomer. 